Wireless multi-hop networks have been widely used in recent years to gather information from numerous wireless terminals which are placed in a wide area. A “wireless multi-hop network” in this context refers to a wireless communication network configured by an access point (which may also be called a “concentrator” or “base station”) and a plurality of wireless terminals.
Information of the respective wireless terminals in the wireless multi-hop network is transmitted directly or via another wireless terminal or terminals (through hops) to the access point (hereinafter referred to as “AP”). The AP then transmits the information gathered from the respective wireless terminals to a center (e.g., a management server of the wireless multi-hop network). As a result, costs incurred by gathering information from multiple wireless terminals are confined mainly to communication costs of communications between the AP and the center, which enables relatively cost-effective information gathering.
When the wireless terminals in the wireless multi-hop network of this kind are placed in a wide area, multiple APs need to be placed to gather information from all of the wireless terminals. When multiple APs are to be placed, the network is allowed to have redundancy by placing more APs, so that reliability in the communications is improved. However, this entails the drawback that a larger number of APs to be placed leads to higher placement costs to place the APs and higher communication costs. Hence, optimization of the placements of the multiple APs is critical to configuring a low-cost wireless multi-hop network while maintaining the reliability of the communications.